Note: Descriptions are shown in the official language in which they were submitted.
~ 1~5297
-- 1 --
SOLVENTS, SOLUT_ONS, AND PRESSURE-SENSITIVE MARK-
RECORDINGASYSTEMS
This invention relates to solvents and solutions which
are useful in the production of pressure-sensitive mark-
recording systems and to such systems themselves~
The most ~amiliar form of pressure-sensitive mark-
5 recording system is the so-called carbonless copying
paper which comprises a two-sheet system in which the
under surface of the top sheet has a coating of micro-
capsules of a solution of a colourless chromogen, while
the upper surface of the lower (receiver) sheet has an
10 absorbent coating including a sensitizing agent for the
chromogen. When a marking instrument is applied to the
top sheet, the microcapsules are locally ruptured,
thereby releasing the chromogen solution from the
affected microcapsules ~o react with the underlying
15 sensitizing agent and form coloured marks on the
receiver sheet corresponding to the marks applied
to the top sheet.
A successful carbonless copying paper system needs
to meet a number of criteria. For example the marks on
20 the receiver sheet should develop rapidly to a leyible
intensity of colour and a legible mark should persist
for as long as the sheet is required to be kept.
Whether the various crlteria are met depends on a number
of factors including the nature of the solvent, the
25 sensitizin~ a~ent and the chromogen, and many different
materials of each category have been proposed. S~lvents
which have been proposed include hydrocarbons, for
instance petroleum fractions or synthetic hydrocarbons,
especially synthetic aromatic hydrocarbons, such as
30 partially hydro~enated terphenyls, and esters,
for instance alkyl phthalates.
:,-
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115S297
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The sensitizing agent is usually an acid clay,
for example an attapulgite or bentonite clay, or an
acidic organic polymer, for examplè a phenolic resin
or a partially or wholly hydrolysed styrene-
5 maleic anhydride or ethylene-maleic anhydride polymer.
The chromogens which are probably most frequently
referred to in the art are the phthalide derivatives,
especially crystal violet lactone. These chromogens
are usually used in solution in a hydrocarbon type
10 solvent. One reason for this choice of solvent is that
although the phthalide colour-formers are soluble in
esters, for example, it is found that esters and
certain other solvents having similar polarity to the
esters, show too great a tendency to compete with the
15 chromogen in affinity or the sensitizing agent, so
that in some cases, no colour development occurs.
This is e;pecially so with acid clay sensitizing agents.
Crystal violet lactone (CVL) is usually used in
conjunction with another chromogen because the colour
20 produced by CVL, although o good initial intensity,
tends to fade on exposure to air and light. Various
chromogens are known having a performance which com-
plements that o CVL (hereinafter referred to as
complementary chromogens) in that, although they pro-
25 duce colours of lowex initial intensity than CVLcolour, their colours are substantially more resistant
to fading, and the colours in ~act intensify under the
conditions which result in the fading o~ CVL colour.
Complementary chromogens which can be used in the
30 present in~ention include benzoyl leuco methylene blue
(sLMs), the carbazolyl aminophenyl methane or carbazolyl
indolyl methane compounds of British Patent Specifi-
cation 1,548,059, the bis- or ~ris(carbazolyl) methane
. . . : . :
. .
: :
11~529'~
compounds of British SPecification 1,550,968 and the
tris-phenylaminophenyl-methane compounds of German
Offenlegungsschrift 2 824 693.
British Patent Specification 1,526,353 discloses
5 a solver.~ for use in pressure-sensitive copying paper
systems comprising a blend of an aromatic hydrocarbon
component and an aliphatic diester component, the
latter be.ing the dimethyl or diethyl ester of succinic,
glutaric or adipic acid or a mixture of two or more
10 such esters, the ester component being present in an
amount of 0.5 to 10 parts by weight per 100 parts by
weight of the aromatic hydrocarbon component. British
Patent Specifica.ion 1,526,353 shows that the presence
of the ester in such solvents improves the rate of
15 colour development of crystal violet lactone on a
sensitizing agent of the phenolic resin type compared
with the rate of colour development obtained usiny
the aro~atic hydrocarbon component alone. The said
Specification, however, also shows that higher alkyl
20 esters and amounts of the ester component in excess
of 10 parts by weight per 100 parts by weight of the
aromatic hydrocarbon component are not effective in
thi3 way.
We have now found that when using an acid clay
25 sensitizing agent and when using crystal violet lactone
(CVL~ in cOnjUnGtiOn with a complementary chromo~en,
such limitations do not apply, beneficial ef~ects of
a different kind being obtained with solvents containin~
relatively large amounts of an ester component.
A solvent of the invention is a liquid comprising
a blend of an aromatic hydrocarbon component and an
ester component, the weight ratio of the two components
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1~55297
in the blend being from 85:15 to 10:90, the aro-
matic hydrocarbon component being a hydrocarbon in
which at least half the carbon atoms are benzenoid or
a mixture of such hydrocarbons, and the ester com-
5 ponent being a diester of the formula
ROOC(C H2 )COORl or R2COO(C H2 )ooCR3
wherein n is an integer, or example from 1 to 20,
R is an aliphatic or cycloaliphatic hydrocarbon
group, Rl is an aliphatic or cycloaliphatic hydro-
10 carbon group or a benzyl or alkylbenzyl group, and
2 d R3 is an aliphahyi~cr/ograra mi ~ure ofsuch diesters, and the solvent having a volatility
and ~iScosity such that it is suitable as a solvent
for the chromogen in a pressure-sensitive mark-
15 recording system.
A solution of the invention is a solution of amixture of CVL and a complementary chromogen in a
solvent of the invention; and a pressure-sensit.ive
mark-recording system of the invention comprises
20 (a) sheet material, (b) mark-forming components supp-
orted by the sheet material and arranged in juxtaposi-
tion but in unreactive condition, the said components
comprising a chromogenic material which is a mixture
o. CVL and a complementary chromogen and an acid `-
25 clay sensitizing agent for the chromogenic material -
which produces a colour from the chromogenic material ~
when brought into contact with the chromogenic mat- i .
erial in the~resence of a liquid solvent of the inven- .
tion and (c~ the said solvent supported by the sheet
30 material ~ut separated from the sensitizing~agent by
a physical barrier which is rupturable on the application
of a marking instrument to the sheet material.
The use or a solvent in accordance wlth the present
'
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1 ~5297
invention generally gives marks having somewhat lower
initial intenslty than those obtained by the use of
aromatic hydrocarbons alone but significantly more
intensity than those obtained by the use of the esters
5 alone. Moreover, when exposed to light, the maxks
develop a maximum intensity after 2-5 days, the maxima
obtained with the blends being higher than those
obtained with either of the individual components.
The aromatic hydrocarbon component in a solvent
10 for use in the present invention can be a single
compound, but is often a mixture of compounds. Examples
include partially hydrogenated terphenyls, for example
hexahydraterphenyls and dodecahydroterphenyls. As
normally produced, materials of this type are mixtures
15 containing, in various proportions, fully hydrogenated
terphenyls, partially hydrogenated terphenyls, and
terphenyl itself. The terphenyl which is partially
hydrogenated in obtaining such mixtures is itself a
mixture of isomers. Commercially available hydrogenated
20 terphenyls include Santosol 340 and Santosol 300, which
are terphenyls partially hydrogenated to different
extents, the latter having a higher degre2 of residual
aromaticity than the former. Other aromatic hydrocarbons
include benzylated and alpha-methylbenzylated alkyl-
25 benzene3, e,g. mono- and dibenzyl ethylbenzene, mono-
and dibenzyl meta- and/or para-xylene, and mono( alpha-
methylbenzyl)toLue~e, alkylnaphthalenes, e.g. dipropyl-
naphthalene and mono-alpha or -beta(2-hexyl)naphthalene,
and alkylbiphenyls, e.g. mono- and di-isopropylbiphenyls.
In an ester of the formula ROOC(CnH2n)COOR each
of R and R can, for example, be an alkyl or alkenyl
group containing up to 18 carbon atoms, arranged in
either a straight or branched chain. Examples of alkyl
~5297
-- 6
groups from which R and R may be selected are isopropyl,
n-butyl, isobutyl, n-hexyl, isohexyl, n-octyl, 2-ethyl-
hexyl, decyl, dodecyl, tetradecyl and hexadecyl, while
allyl and 4-methylpent-2-enyl are examples of alkenyl
5 groups.
When R or Rl is a cycloaliphatic hydrocarbon
group, it is generally-a cycloalkyl or alkyl-substituted
cycloalkyl group containing from 5 to 10 carbon atoms,
for example cyclopentyl, cyclohexyl or a methyl-
10 cyclohexyl group, although the corresponding cyclo-
alkenyl groups are also contemplated.
Alkylbenzyl groups from which Rl may be selected
are usually those wherein the alkyl substitu-tion occurs
in the benzene nucleus. Preferably the number of
15 alkyl substituents does not exceed three, and each
such substituent contains up to three carbon atoms;
more preferably, the total number of carbon atoms in
the alkyl substituent or substituents does not exceed
four. ~xamples of alkylbenzyl groups are 2-, 3-, and
~-methylbenzyl, 4-ethylbenzyl, 4-isopropylbenzyl and
2,4-dimethylbenzyl.
When both R and R are alkyl or alkenyl groups
each preferably contains from 4 to 16, more prefer-
ably from 6 to 12 carbon atoms. When Rl is a benzyl
25 or alkylbenzyl group, R is preferably an alkyl or
alkenyl group containing from 8 to 1~ carbon atoms.
The grouping CnH2n in esters of the formula
ROOC(C H2 )COOR is preferably a straight chain group-
ing, but it may be branched, Preferred esters of the
30 formula ROO~(C H2 )COORl are those wherein n has a value
of from 2 to 8, i.e. ~where C H2n is a straight chain
grouping) the succinates, glutarates, adipates, pime-
lates, suberates, azelates and sebacates~ Particularly
.
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1~S5~97
-- 7 --
good results have been obtained using mixtures of esters
known as "nylonates", which are obtained by the esteri-
fication of mixtures of succinic, glutaric and adipic
acids, especially with aLkanols or mixtures of alkanols
5 having from 6 to 12 carbon atoms, for example with a
mixture of C7 to Cg alkanols or with a mixture of
C8 to C10 alkanols- .
Examples of individual diesters of the formula
ROOC(C H2n)COORl are di(2-ethylhexyl) succinate, n-butyl
10 2-ethylhexyl glutarate, allyl 2-ethylhexyl glutarate,
di-isodecyl glutarate, di-isobutyl adipate, diallyl
adipate, dicyclohexyl adipate, diisooctyl adipate,
di(2-ethylhexyl)adipate, benzyl isobutyl succinate,
benzyl isobutyl glutarate, benzyl isodecyl glutarate,
15 allyl benzyl adipate, benzyl cyclopentyl adipate,
diisobutyl pimelate, di-isopropyl suberate, diethyl
aæelate ~nd di-sec-butyl sebacate.
In esters of the formula R2COO(CnH~?OOCR , each
of R and R can be, for example, an alkyl or alkenyl
group of up to 18 carbon atoms arranged in either a
straight or branched chain. Preferred groups are
alkyl groups of from 1 to g carbon atoms, for example
methyl, ethyl, isopropyl, isobutyl, sec-butyl, n-pentyl,
isopentyl, hept-3-yl and n-nonyl. In preferred esters,
n has a value from 2 to 10, and the grouping CnH2n
may be straight or branched, Branched groupings are
preferred when n has a value of 4 or more such that not
more than 4 carbon atoms separata the two oxygen atoms
linked to the grouping CnH2n, as for example in esters
of 2,2,4-trimethylpentane-1,3-diol.
Examples of individual dlesters wnich can be used
are ethylene glycol dipropionate, ethylene glycol
diisobutyrate, propylene-1,2 glycol di-sec-pentoa.te,
butylene-1,4- glycol diproponate~ butylene-1,4-glycol
~.,
''' ~ ' 1
~1552g7
dimethacrylate, hexamethylene glycol diacetate,
2,2,4-trimethylpentane -1,3-diol, l-acetate,
3-isobutyrate, 2,2,4-trimethylpentane-1,3-diol
diisobutyrate, 2,2,4-trimethylpentane-1,3-diol,
5 1-isobutyrat~e,3-sec-hexoate, and 2,2,4-trimethylpentane
-1,3-diol, l-isobutyrate, 3 n-octoate.
In solvents of the invention which are blends
of an aromatic hydrocarbon and an ester or a mix-
ture of esters of the formula ROOC~CnH2n)COOR , the
lO hydrocarbon component and the ester component are
preferably present in proportions by weight from
60:40 to 15:85, and even more preferred are blends
in which the proportions are from 50:50 to 20:80,
for example a blend of from 25 to ~5 parts by weight
15 of the aromatic hydrocarbon component with from 75
to 65 parts by weight of the ester com~onent.
Where the ester component i5 an ester or a
mixture of esters of the formula R2COO~CnH2~)00CR ,
the aromatic hydrocarbon component and the ester
20 component are preferably present in proportions from
80:20 to 20:80, for example from 75:25 to 50:50.
The liquid solvent used in the present invention
may consist of the blend of the components as defined
above, provided its physical properties, e~g.
25 viscosity, are suitable, or it may be a mixture of
the blend with one or more other miscible liquids.
Such other liquids include inert diluents, ~or example
mineral and vegetable oils, such as kerosene, paraffin
oil, castor oil, soybean oil, and corn oilq Also
30 useful as diluents are (long-chain alkylated) benzenes,
for e~ample (C7-~l6 alkyl) benzenes. A diluent
functions to alter such physical properties of the
solvent, for instance viscosity or vapour pressure,
as may be desired for optimum handling or processing.
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~5297
A solvent of the invention preferably contains at
least 50~ by weight of the blend, but in some
instances, the blend may be diluted with up to, for
example, 3 times its own weight of diluent. For
rapid development of print intensity, the solvent is
preferably one having a viscosity in the range 5 to
15 centistokes at 33C. Blends of the invention
can usually be ~ormulated without the use of diluents
to give solvents having satisfactory viscosity charact-
10 eristics, even at relatively low temperatures. Thisis an advantage of the blends over the aromatic hydro-
carbons which are in ~ y instances highly viscous below
OC .
In the solutions of the invention, the proportions
by weight of CVL and the complementary chromogen in
the mixture can, f-or example, range from 10:90 to 90:10
Preferred proportions by weight are, however, from
25:75 to 75:25, more especially from 40:60 to 60:40.
The concentration of the mixture in the solution may
be as low as 0.1% by weight, bu~ will usually be at
least 0.5~ by weight. The optimum concentration will
vary with the particular solvent and the sensitizing
agent, but is usually not in excess of 5~ by weight,
and is often in the range 2% to 4% by weight.
Higher concen~rations of the mixture, for example up
to 10~ by weight can be used, however, an advantage of
the present solvents being that they have greater
solvent power for mixtures of CVL and the complementary
chromogen than have the aromatic hydrocarbon components
alone.
The acid clay used as sensitizing agent for the
chromogenic material in the present invention can be
any of those conventionally used for this purpose,
1 1 5~297
-- 10 --
including bentonite and attapulgite. The naturally
occurring clay may be subjected to various treatments
such as acid extraction or calcination before use as
the sensitizing agent.
Several encapsulation systems have been pro-
posed for the encapsulation of the chromogen solution
for use in carbonless copying paper, and the capsule
walls in such systems generally may be formed from
either natuxal or synthetic polymeric material. In
10 the present invention, the capsule wall or shell is
preferably made from a synthetic polymer, for example
a polyurethane resin, a urea-formaldehyde resin, a
melamine-formaldehyde resin or a polyamide resin~
The use of such resins as shell-forming material in
encapsulation is described in, for example, U.S.
Patent 3,016,308, British Patent 989,264 and U.S.
Patent 3,429,827. Shells of this kind can be made
significantly less permeable to the esters used in
the present invention than shells made of natural
polymeric material such as gelatin.
The mark-recording system of the present
invention can be prepared according to well known
conventional procedures. Descriptions of methods for
preparing both the chromogen carrying paper and clay-
coated receiving paper are to be found in the liter-
ature.
Although a preferred embodiment of this inven-
tion comprises a two-sheet system wherein the acid
clay is carried by one ~heet and a marking 1uid
comprising the chromogenic material and solvent is
carried by a second sheet, the invention is not limited
to such systems alone. The only essential require-
ment is that the chromogenic material and the acid clay
. . .
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1 ~5529~
be maintained in a sepa ate or unreactive condition
until pressure is applied to the system,and that upon
the application of pressure the chromogenic material
and acid clay are brought into reactive contact. Thus
5 it is possible to have the chromogenic material and
acid clay present in a dry and unreactiv~ state on a
common carrier and to have the solvent alone carried
on a separate sheet,whereupon the application of
pressure would release the solvent into the chromogen-
10 acidic material mixture and promote localized reactionand colour development Obviously, many other arrange-
ments, confisurations and relationships of the solvent
and the mark forming materials with respect to their
encapsulation and location on the supporting sheet or
15 webs can be envisaged, and suc'n arrangements are within
the scope of the present invention. For example, it
is possible to coat a sinyle paper or support member
with all the components of this system to form a
single self-contained unit which can be marked by
20 the movement of a stylus or other pressure-imparting
- means upon the surface of the paper. Such papers
are particularly useful for ~Se in inkless recording
instruments.
Solutions of the invention were evaluated by
25 the following techniques ;
A solution of a mixture of CVL and the comple
mentary chromogen in the solvent was prepared. To
estimate print intensity, a plate engraved with a
pattern of dots was coated with sufficient of the
30 solution to give a coating 18 microns in thickness,
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115529~
- 12 -
using a doctor blade. A carriage-supported roller
having a paper sheet coated with an acid clay sensitiz-
ing agent wrapped around the roller was then moved
slowly across the solution-coated plate under constant
5 pressure. Colour developed on the paper. The paper
was removed from the roller, the intensity of colour
was measured, using equipment described below, at 20
different points on the paper surface and the values
were averaged. After the intial reading, the paper
10 was exposed to UV light using conventional laboratory
equipment having four 15 watt U.V. sources, principal
wave-lengths 254 and 366 mm, used to study colour
fading under U.V. irradiation. It was removed at
intervals for further colour intensity measurements,
15 average values being obtained as beore.
The results given in Tables 1, 2 and 3 below
were obtained with a Macbeth RD 514 reflectometer
calibrated against a "perfect wh te" of 0.07 units
of optical density and a "perfect black" of 1.78 units
20 of optical density, using standard "perfect white"
and "perfect black" plates supplied by the manufacturer.
With thls reflectometer, the higher the reading, the
greater the intensity, The results given in Tables
and 5 were obtained using a Neotex Tru-Color XX
25 Colorimeter to obtain the Y coordinate (brightness)
value of the ~IE colour, so tXat the numerical values
presented are inversely related to colour intensitv.
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1 15529~l
- 13 -
The following abbreviations are used :
AGS. A mixture of adipate, glutarate and
succinate esters.
PHT. Partially hydrogenated terphenyl obtained
by hydrogenating terphen.~l using about
40~ of the amount of hydrogen required
for complete hydrogenation.
BMX. Benzylated meta-xylene.
TXIB. 2,2,4-Trimethylpentanediol 1,3-diisobutyrate.
For the results shown in Tables 1-4, the
solution was a 3% by weight solution of a mixture
of equal parts by weight of CVL and BLMB. The
results of Table 5 were obtained using a 2% by
weight solution of a mixture of equal parts by
weight of CVL and a carbazolyl methane chromogen
of the class described in British Patent Specifi-
cation 1,550,968.
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1~55297
- 14 -
TABLE 1
Time (hrs~l 0 ¦ 24 ¦ 96 ¦ 144 T 290 ¦ 424
~ I . I I I . I, .
Solvent \ INTE~ ISI7Y I ~EADINGS .
100% Di(C8-Clo)
AGS 0.37 0.72 0.75 0.71 0.68 0.64
7:3* D (C C ) 0.53 0.52 0.75 0.80 0.75 0.70
4:6* Di(~8 C10~
AGS/PHT 0052 0.80 0.72 0.67 0.58 0.55
PHT O . 57 O. 65 O . 52 0 50 O. 47 O . 44
** A mixture of C8,Cg and ClO alkyl groups
* Weight ratios
These results show that the AGS/PHT blends gave
over 90~ of the initial intensity of 100 PHT, whereas
the initial intensity given by the ester component alone
was only 65% of that of 100% PHT. Colour development
during W irradiation showed a maximum for the 4:6
AGS/PHT blend af~er 24 hours, and a maximum for the
7:3 AGS/PHT blend after 144 hours, both maxima being
higher than the maxima shown ~y the Nylonate alone
or PHT alone.
Table 2 gives the colour intensity values obtained
using blends of dialkyl esters and PHT in the weight
ratio 7:3 in comparison with PHT alone.. The results
are expressed on a scale on which the initial colour
intensity using PHT alone as the solvent is set at
100 .
.
~55297
- 15 -
TABLE 2
\ T'n~ s~ O ¦ 22 1 42 ¦ 70 ¦ 112 ~ 159
Solvent \ INTENSITY VALUES ,
~ . _ .
Di(2-ethylhexyl) 76.8 147.3 150.6 166.0 159.3 156.2 144.0
AGS/PHT .
Di(C~-Cg alkyl) 71.6 144.9 148.3 166.1 159.5 155.0 141.0
PHT 100 129.1 114.5 120.2 103.6 98.4 90.2 .
The results in Table 2 show a similar effect to that
demonstrated in Table l, with a lower initial intensity
for the blends than for PHT alone, but with the blends
showing a significantly higher maximum intensity.
Moreover, this relatively higher intensity persists
af,ter the onset of fading.
Table 3 gives the results obtained using blends
o~ benzyl alkyl esters with PHT in the weight ratio 7:3
in comparison with a blend of kerosene and PHT in the
weig~t ratio 7:3 and PHT alone. The intensity values
are given on a scale on which the initial intensity
obtained with PHT alone is expressed as 100
TABLE 3
20Time (hrs) 0 1 20 1 86 1 110
~ _ __._ I ., . I ~ I . .
Solvent ~ .INTENSIT'x' VA~UES 1.
~ ~ . . .
Benzyl isobutyl 63.8 103.1 124.9 125.1
succinate/PHT
Benzyl isodecyl 94.6 126.7 130.2 130.5
glutarate/PHT
Kerosene~PHT 110.8 118.3 106.8 105.2
PHT 100
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~5297
_ 16 -
Table 4 gives results obtained using blends o~
equal parts by weight of AGS and PHT, and of AGS
and BMX in comparison wi-th PHT alone.
TABLE 4
~ - . .. ._.. . ~
Time (hrs) 0 90
~ . . ~ ..... , .. _ _
Solvent Lightness (Y) CIE Color space
_ A _ _. __ _
Di(c8~loalkyl)AGs/pHT 41.6 10.8
Di(c8-cloalkyl)AGs/~x 38.2 10.4
PHT 33.7 11.8
. ... . _ _ ... .__ .... .
Both the AGS/PHT and the AGS/BMX blends gave greater
print in-tensity after 90 hours UV exposure than PHT alone.
TABLE 5
~ . ....i_
~ me (hrs) 0 ¦ 24 ~ 48
Solvent \ Lightness (Y) CIE color Space
7:3*PHT/Di(C7-C9 . ~ _ _
alkyl)AGS 22.4 ~18.4 17.5 17.9
7:3*PHT/TXIB 25.3 11.5 10.8 11.6
7~3*PHT/Kerosene 19 2 13.2 17.3 20.2 .
* Weight ratios
The PHT/TXIB mixture showed particularly good
results, and both ester blends gave greater print
intensity after 72 hours UV exposure than the PHT/kero-
sene blend.
